# CVE-2026-81905: Business logic in Concrete CMS

> Attackers can redeem validation hashes for unintended purposes, enabling account takeover or activation if hashes are exposed via other channels.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 10 Sep 2026
- **Updated:** 11 Sep 2026
- **Also known as:** GHSA-xgp3-243g-wxvm

## What is CVE-2026-81905?

CVE-2026-81905 is a medium-severity vulnerability in Concrete CMS, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Concrete CMS below 9.5.3 stores user validation hashes for multiple purposes (email/registration validation, password reset, and persistent login) in a single table with a type column, but the redemption path resolves a hash by value alone and does not verify its type. As a result, a hash issued for one purpose can be redeemed for another: a long-lived registration hash (60-day expiry) can be submitted to the password-change endpoint to set a new password on the target account, and a password-reset hash can be submitted to the email-validation endpoint to activate an account. Exploitation requires the attacker to first obtain a valid hash through a separate channel (for example email interception, log exposure, or SSRF against an internal mail relay), so the flaw amplifies the impact of any hash disclosure rather than creating a standalone entry point. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 6.3 with vector CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Yonatan Drori from Tenzai for reporting.

Weakness: CWE-863 (Incorrect Authorization), CWE-640 (Weak Password Recovery Mechanism for Forgotten Password)

## Which versions are affected by CVE-2026-81905?


## How do I fix CVE-2026-81905?

No fix has been published for CVE-2026-81905 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-81905 being exploited?

There is no known exploitation of CVE-2026-81905 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81905 and fix it if it is affected.

What it is: CVE-2026-81905 is a medium-severity vulnerability in Concrete CMS, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-81905 in the wild and no public exploit code.

Affected product: Concrete CMS. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-81905/ (Markdown: https://insights.sbomify.com/CVE-2026-81905/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81905
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81905
- OSV: https://osv.dev/vulnerability/CVE-2026-81905

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81905/
Summaries are generated and may contain mistakes; the official description above is the record.